1. Field of the Invention
The present invention relates to a device and to a method for detecting fog using spectroscopy.
2. Description of the Related Art
For the detection of interference with visibility in a vehicle, that is caused particularly by fog, some methods exist in the related art for detecting fog.
A device is known from published European patent application document EP 1498721 A1 which takes images in the travel direction, using a camera in a vehicle. An image of this camera is evaluated as to whether there is at least one pixel which falls below a brightness value, i.e. is dark. Because of the scattered light effects when there is fog present, one may assume that all pixels have a minimum brightness, and consequently permit the conclusion that there is fog.
Furthermore, camera systems are known for use in a vehicle for detecting fog, which require an active element (such as infrared-LED), for example published European patent application document EP 2020595 A1.
Another method is the detection of fog based on the detection of objects and perhaps their distance. Published European patent application document EP 1826648 A2 compares the edge thickness of detected objects with those in a database, and derives from this the visibility conditions and rain or fog. This works only as long as objects are present and these are described in the database.
A more detailed method is described in published European patent application document EP 2056093 A1, in which the gray values distribution is examined in a certain area of the image, particularly on the horizon. However, this method may lead to false detection in the case of other weather conditions that result in the same physical effect on the image, a possible example for this being snow cover on the landscape and the road.
Moreover, there is voluminous non-patent literature that also speaks to the topic of fog detection.
Up to now, there does not, however, appear to exist fog detection using image-generating methods (video), without the distance (visual range) being determined, especially the distance from other objects or at least a hypothesis on this.